The preferred embodiment relates generally to a case that contains the components of a power transmission for a motor vehicle, and particularly to an vent apparatus for allowing air to enter and leave the case while preventing ingress of water and contaminants to the case.
A sealed transmission case requires a vent due to changes that occur in the temperature of the air held in the transmission case. The equation of state or characteristic equation of a perfect gas, derived from Boyle's law and either of Charles' laws for an ideal gas, states p*V=w*R*T, wherein p is gas pressure, V is gas volume, w is weight of the gas, R is the gas constant, and T is gas temperature. If the volume of air in the transmission case is constant due to the case being sealed, then changes in the temperature of air in the transmission case would cause pressure within the case to increase and decrease. If the transmission case were not vented and the temperature of air in the sealed volume of the case were increased, air pressure within the case would increase. That increase in air pressure in the case could cause transmission fluid to be forced from the case through the fill tube provided to add transmission fluid to the case. A decrease in air pressure could cause water or contaminants to enter the case past external transmission seals. Therefore, a transmission case is vented to maintain a zero pressure differential between its interior and the ambient, atmospheric air pressure.
However, venting the transmission case to allow air to enter the case through a vent while preventing water and contaminants from being drawn into the transmission case presents challenging technical issues. There is a need to provide a simple, inexpensive, yet reliable technique for admitting air through a vent and excluding water and other contaminants from entering the transmission case through the vent.